Another flag bites the dust. This time: -ffinite-math-only.

Another flag bites the dust. This time: -ffinite-math-only.

Since GCC 5, with this flag set, NaN compares equal to zero in some cases but
not others. Causes e.g. "attempted division by zero" error spam from this QC
code:

float x = nan("");
if (x == 0) {
  return 0;
}
return 1.0 / x;

Yes, those NaNs should not be happening in the first place, but suddenly
passing some but not all equality checks to zero seems rather dangerous.

Reference: issue #2412 (not a fix for it; the QC code has a problem too but
this change helps track it down properly).

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12522 d7cf8633-e32d-0410-b094-e92efae38249
::stable-branch::merge=f96918f02808e35a2cd94885003c24a145be5bb9